The correct answer is: "negative utility".
The utility of the first candy, the satisfaction that the consumer gained when eating the bar is very large . Absolute utility continues growing with each extra bar eaten, although the size of the utility increase is lower from the 3rd to the 4th bar, than from the 1st to the 2nd. Absolute utility grows because more utility is accumulated by each extra bar eaten, but marginal utility gained by passing from one to the next is lower each time.
If the amount of bars consumed is extremely large it can end up generating negative utility. It means that the extra bars up a point, do not bring satisfaction but insatisfacion. In this example, it is easy to imagine the stomachache you might probably have after eating 15 chocolate bars. and hence the negative satisfaction that the consumer would experience.